1. Field of the Invention
The present invention relates in general to lock-up torque converters and more particularly to a device for controlling relative rotation, i.e., slip between input and output elements of a lock-up torque converter.
2. Description of the Prior Art
Since the torque converter is adapted to transmit power by way of working fluid, relative rotation between the input and output elements is inevitable, resulting in a lowered power transmission efficiency. For this reason, there have been heretofore proposed, as disclosed by U.S. Pat. No. 4,002,228 and Japanese Patent Publication No. 59-747, a clutch slip control technique for controlling the above described relative rotation in accordance with the turbine torque of the torque converter (i.e., torque transmitted by the turbine hub) and, as disclosed by U.S. Pat. No. 4,169,526, a clutch slip control technique for controlling the above described relative rotation in such a manner that the ratio of the turbine torque and the torque transmitted by the clutch is maintained constant. The aforementioned clutch slip control techniques, however, have not met with entirely satisfactory results. In some cases, the techniques cause undesirable noise, vibration, and a decrease in fuel efficiency.